Accelerator for the vulcanization of rubber and method of making the same



I Patented Oct 26, 1926.

UNITED STATES PATENT OFFICE.

LORIN n. SEBRELL, or Axaon, OHIO, AssIeNoa TO THE GOODYEAR TIRE & RUBBERCOMPANY, or AKRON, OHIO, A conroaa'rron or OHIG.

ACCELERATOR FOR THE V'ULCANIZATION 0F RUBBER AND METHOD OF MAKING THESAME.

No Drawing. Application filed April 4 My invention relates toaccelerators for the vulcanization of rubber and rubber compounds', andit has, for its primary Ob ect, the provision of a method which shall be5 especially efiicient for the production of such materials.

It has been suggested heretofore that certain thiazole compounds provideefficient ac-' celerators for the vulcanization of rubber.

. These accelerators are especially desirable it is possible,

because of theirpower, since they possess an ability to promote thevulcanization of rub- ,bermuch more rapidly than many accelerators nowknown. By reason of this ability,

if desired, to reduce the temperature of vulcanization, which has beenfound to improve the hysical characteristicsof the vulcanized rub er.Moreover, certain of the thiazoles also appear to improve the agingcharacteristics of. rubber or rubber NH (Kiri N FE OSg+S- Men:

an s

V a H NHI -o-m g (2) +os,-- g V 1924. Serial No. 704,159.

compounds, which, of course, is a particularl desirable feature.

T e principal object of my invention is to i provide a method whichshall result in production of the several mercaptobenzothiazoles totheexclusion of products of side reactions, which are not desirable. Forexample, in the formation of l-mercaptobenzothiazole from a reaction ofaniline, carbon disulfide and sulfur, it is possible for the reaction togo in two different ways, one of which results in the roduction ofanilidobenzothiazole, which is an alkali insoluble compound that has noaccelerating effect upon rubber if compounded therewith. Consequently,it is desirable to avoid the production of this material in conjunctionwith the formation of mercaptobenzothiazole. aniline, carbon disulfideand sulfur isindicated by the following formulae:

' SE i NH 0 I a 11+ s o-amoai Has (0) side reaction product is quitelarge, form ing, in some experiments, as high as 60% of the totalroduct. i

The primary feature of my invention is to ,first form a stable compoundfrom the amine, which' is initially utilized to produce the particularmercaptobenzothiazole, and subsequently, to cause a reaction with thisstable compound and sulfur to form the product desired. By first forminga stable compound, in many cases, it is possible to secure higher yieldsof thedesired mercaptobenzothiazole derivative, because undesirableby-products are not formed. My method of The reaction of' producingaccelerators applies equall well to mercaptobenzothiazol'es other than te one The tem rature and pressure, that obtain in the pr uction of thematerial, may vary over wlde ranges, with no substantial difference inthe result obtained. If the pressure is not relieved by permittinghydrogen sulfide to escape, which is formed during the reaction, it willrise quite high. For example, in the production of the accelerator,indicated in the above equation, with a maximum temperature of 224 0.,the pressure rises to 1000 lbs. per sq. inch. However, it is desirable,if not essential, that the temerature be at least 100 C. to securesatisactory results, and a pressure of at least 100 lbs. per sq. inch isalso necessary to secure a yield of material within the scope ofpractical operation. Somewhat higher temperatures and pressures will befound more eflicient, but the last mentioned are 1 operative. Forexample, I have found that very satisfactoryresults may be obtainedemploying a temperature of between 175 an 250 0., which will probablyresult in a pressure in the neighborhood of 600 to 1000 lbs. per sq.inch. llhe material is subjected to eat until the rate of increase in'pressure becomes substantially constant, which indicated that thereaction has fully occurred,

The zinc salt of phenyldithiocarbamic acid may also be employed to form,by reaction with sulfur, l-mercaptobenzothiazole, and

very eflicient production of the material will result. As a matter offact, zinc may be utilized to replace ammonia in the production of allthe mercaptobenzothiazoles men- 'inonium salts in general.

tioned herein, although I prefer the am- With the zinc salts, highertemperatures may be utilized,

with lower pressures in pounds per sq. inch with one molarequivalent ofsulfur, and placed in an autoclave, where heat and-pressure are appliedto produce l-mercaptobenzothiazole. It is, of course, possible,-also, toproduce the thiazole by merely admixing ammonia, as a gas or dissolvedin water, with phenyldithiocarbamic acid and sulfur, and heating themixture in an autoclave, or other suitable'vessel. This is, of course, amore direct method, and will produce very satisfactory results, probablybeing the manner in which the accelerators will be manufactured incommercial quantities. However, substantially the same reactions occur,namely, the ammonium salt is formed, which then rgacts with sulfur toproduce the mercaptobenzotliiazole. This reaction may be represented asfollows:

carbamic acids may be employed to form the thiazoles mentioned herein.These constitute examples of monovalent metallic salts that may beutilized in addition to the bivalent metallic salts, such as zinc andlead.

The sodium and potassium salts are em ployed in the same manner as thezinc and ammonium salts, and consequently, descriptions of reactionsembodying the atter may beapplied to the former.

In the production of l-mercapto-3-methyl benzothiazole, an ammonium saltof orth0-.

tolyl-dithiocarbamic acid, orfa zinc salt of the same acid, is employedto produce this accelerator. Substantially the same respectivetemperatures and pressures may be employed in the reaction of thesematerials with sulfur to produce the accelerator, but, asaforementioned, wide variations in the temperature and pressure mayexist, without detrimental effect upon an eflicient production ofmaterial.

In the production of l-mercapto l-methylbenzothiaz ole, the ammonium orzinc salt of meta-tolyl-dithiocarbamic acid is employed.

enzothiazole, the ammonium or zinc salt To obtain 1-mercapto-5-m'ethylofpara-to] l-dithiocarbamic acid is utilized'lls to react with sulfur. Thelast three mentioned mercaptob enzothiazoles have been previouslysuggested as being d accelera-' 1 tors, but the particular metho oftheir production, by utilizing the ammonium or zinc salt of thecorresponding aryl dithiocarbamic acid, has not been contemplated to thebest of my knowledge,

I have discovered another mercaptothiazole which has not been mentionedheretofore, and one that provides exceptionally goods results in thevulcanization of rubber' or rubber. compounds. 1-mercapto-3-5-vdimethyl-benzothiazole is a new compound other materials, vary overwide ranges, but

in this instance, as 1n the others, it 1s preferable to emplriy atemperature in excess of 100 (1., an have obtained efiicient' re-.

'sults with a temperature in-the neighborhood of 250 C. with either thezinc. or ammonium salt. The pressureresulting from the ammonium saltreaction will be probabl from 1000 lbs. to 1200 lbs. per sq. inch,

. an with the zinc salt, a somewhatvlower pressure will be established.These pres- .sures are established, of course, if hydrogen sulfide isnot released during the reaction, butlower pressures may be emplo ed byreleasing some of the hydro en sul do, without detrimental eflect on t eproduction, or

the percentage of yield. For instance, if the pressure he maintained ata proximately 700 to 800 lbs, per sq. inch, goo results may The otherthiazoles are named in the same be attained.

Another accelerator which is also new'in the art, to the best of myknowledge, is 1- mercapto-b-ethoxybenzothiazole. This latter acceleratormay be formed from the reaction of sulfur with the ammonium or zinc saltof para-phenetyl-dithiocarbamic acid.

Still another new compound of this gen-. eral class of accelerators,1-mercapto-5-methoxybenzothiazole, may be formed from the reaction ofammonlum or zinc salt ofpara methoxy-phenyl dithiocarbamic acid withsulfun- As an example of a use of the new mercaptobenzothiazolesmentioned herein, the

- following compound may be employed with any of the last threeaccelerators mentioned, in substantially the proportions set forth 100parts rubber, 5 parts zinc oxide, 3.50 parts sulfur, 1.00 parts of thel-mercaptoenzothiazole or its analogs.

The "foregoing compound may be vulcanized at a temperature correspondingto 40 lbs. of steam pressure in from 5 minutes'to 1 hour, depending uponthe thiazole used. A temperature corresponding to 20 lbs. of

steam pressure may also be used, but the time of cure is increased as aresult. For

more detailed information, reference may be made-to the October 1923publication of industrial and Engineering Chemistry, vol.

15, page 1009. X

The zinc, lead, cadmium, mercury and ammonium salts of the last threethiazoles may be utilized to advantage in promoting the vulcanization ofrubber compounds.

The reaction products of these thiazoles,"

with various bases, bothorganic and inorganic, may also be employed insuch capacity. The disulfides and polysulfides of these thiazoles alsoconstitute accelerators of high power, and the example above given willserve to illustrate a suitable method of employing any of theaccelerators. Of course, the proportions given may be varied somewhat,depending upon whether a very fast curing compound is desired, or onethat cures or vulcanizes at a moderate rate. The

sodium or potassiumsalts of these accelerators may be employed andsuchsalts are examples of monovalent metallic salts as distinguishedfrom the bivalent metallic lows fashion.

t will be appreciated that the method of producin the various 'thiazolesis broadly concerne with the employment of the am- .monium and variousmetallic salts of the corresponding arvl dithiocarbamic acids, whichmust be employed to produce the particular thiazole desired. Althoughthe method contemplates the utilization of heat and pressure, it will beappreciated that no exact limits can be practically specified. It issulficient to note that a temperature of at least in excess of 100 C. isdesirable, if not necessary, and that a pressure of at least 100 lbs.per sq. inch should be utilized. However, the pressure may mount as highas 2000 lbs. or 3000 lbs. per sq. inch, depending upon whether suchpressures are practical with the apparatus thatmay be employed. It is,of course, somewhat more practical to utilize a suitable temperature,such, for example, in theneighborh'ood of 250 C. to 300- 6., and allowmgthe pressure to mount to about 700 to 800 lbs. per sq. inch. Ordinarilythe pressure is relieved at intervals to maintain it nearly constant,and when the rate of increase thereof becomes practically constant, thereaction is complete. However, if desired, temperatures as hi h as 350C. to 400 C. may be employed, ut probably the pressure would have to beredueedfrom that established by l lbs. per

such temperature. The temperatures are, of course, limited to such aswill not destroy the material by charring.

Although I have specifically described a method of forming variousthiazoles, it will be appreciated that the exact procedure set forthmaybe subject to minor changes, and that the materials named may suggestother materials that may be employed within the scope of my invention. Idesire, therefore, that no limitations shall be imposed, except such asare indicated in the appended claims.

What lclaim is: 1. A method of producing a Inercaptobenzothiazole whichcomprises forming a salt of an aryl dithiocarbamic acid, admixing sulfurtherewith, heating the mixture to a. temperature of between100 C. and400 C. and maintaining a pressure of not less than 100 lbs per sq. in.nor more than 3000 sq. 1n. 2. A method of producing amercaptobenzothiazole which comprises forming a monovalent salt of anaryl dithiocarbamic acid, admixing sulfur therewith, heating the mixtureto a temperature of 'between 100 C. and 400 C. and maintaining apressure of not less than 100 lbs. per sq. in. nor more than 3000 lbs.per sq. in.

3. A method of producing a mercaptobenzothiazole which comprises formingan ammonium salt of an aryl} dithiocarbamic acid, admixing sulfurtherewith, heating the mixture to a temperature of between 100 C. and400 C. and maintaining apressure of not less than 100 lbs. per sq in.nor more than 3000 lbs. per sq. in.

4:. A method of producingl-mercapto-S- methyl-benzo thiazole which.comprises admixing ammonium o-tolyl-dithiocarbamate with sulfur heatingthe mixture to-a tem-. perature between 17 5 C. and 300 C. andmaintaining a pressure between 500 and 1000 lbs. per sq. in.

5. A method of producingVmercapt-o ary thiazoles which comprises forminga salt of the corresponding aryl dithiocarbamic acid,

mixing sulfur therewith and subjecting the mixture to a positivepressure. and an elevated. temperature not to exceed the'decom positiontemperature of the product.

In witness whereof, I have hereunto signed my name.

LORIN B. SEBRELE.

